Internal shield and seal structure for vacuum sealed switch envelope



June 1965 J. 5. JENNINGS INTERNAL SHIELD STRUCTURE FOR VAGUUM SWITCH; ENVELOPE Film May 2]., 1962 w w 1 m x x I 0 5 \a a) 1.4;, U p H M M 3 3 w 1 4 I 4 4 W 5 4 2 o 7 Q 5 v 4 w r 5 5 2 a .5 5 w x 5 5 5 3 mm m M M MW m wl M w a W w. w M

United States Patent 3,18%,7 INTERIQAL SHEELD SEAL STRUQITURE FGR VAUUUM SEALED SWETCH ENVELQPE Jo Emmett leanings, San Jose, (Tahiti, assignor to Jennings Radio Manufacturin Corporation, @an dose, Qaliti, a

corporation of Delaware Filed May 21, 1962, Ser. No. $6,125 6 Qiaims. 'Cl. Ztltl-ld-d) This invention relates to high capacity vacuum switches and more particularly to the construction of the envelope shield of such switches so as to preserve the efiiciency of the switch against its tendency to break down due to vapor condensation resulting from arcing at the contacts.

The invention also contemplates the improvement of vacuum switch envelope construction to more effectively withstand the extremely high atmospheric forces exerted thereon and at the same time provide an etfective hermetic seal.

A primary object of the invention is the provision of an improved shielding means for effectively preventing vapor condensation on the envelope and which shielding means is easily assembled from relatively inexpensive parts.

Another object of the invention is the provision of an envelope for vacuum switches of very large capacity. By the present invention the construction of the envelope is such as to withstand the very high atmospheric forces thereon and at the same time provide an effective seal which acts as an expansion joint and at the same time is not required to resist the high atmospheric forces which might otherwise impair the sealing function.

Other objects will be brought out in the following description of the invention. I do not limit myself to the showing made by said description and the drawings, since I may use variant forms of the invention Within the scope of the appended claims.

FIG. 1 is a half sectional View of a switch embodying my invention;

FIG. 2 is a greatly enlarged fragmentary sectional view of the sidewall of the switch housing and an associated shielding member;

FIG. 3 is a greatly enlarged sectional view showing a modified form of sealing diaphragm, and

FIG. 4 is a fragmentary horizontal section as taken in a plane indicated by lines 44 of FIG. 1.

In broadly descriptive terms, the switch of this invention and as illustrated in the drawings comprises a cylindrical shell of insulating material such as glass or ceramic material closed at its opposite ends by relatively heavy end plates of conductive material such as copper to which the circuit connections are made.

The fixed contact of the switch is secured to one end plate while the mobile contact is carried by an operating stem or rod around which is arranged a bellows for permitting linear movement of the mobile contact and at the same time preserving the hermetic seal. Atmospheric pressure tends to close the circuit by urging the mobile contact into abutment with the fixed contact. At the junctures between the cylindrical shell and the end plates, annular seals are provided connecting the shell with the adjacent end plates.

The arrangement of parts in the seals is such that in the event a part within the envelope must be replaced or repaired, the membranes may be cut to give access, and then rejoined and the envelope again exhausted for further use.

In detail, the switch comprises a cylindrical glass shell 10 which is interposed between opposite endwalls ll, 12. Said opposite endwalls are formed from conductive material such as copper and the cylindrical sidewalls may be formed of Pyrex glass or other suitable ceramic nonconductive material. Mounting holes 13 and 14 on endplates ll, 12 respectively may be employed for mounting the switch as desired and for connecting the same with appropriate conductors in the circuit involved.

The endplate 11 which comprises the fixed end of the switch is provided with a central depression and a relatively heavy integral block 15 which has formed therein a passageway 16 communicating between the interior of the switch envelope and a tube portion 17 which is closed by the usual tabulation 1%. Vacuum pump means is con nected to tube 1'7 to create the vacuum within the envelope and the tabulation 1% provides a seal after evacuation of the envelope has been accomplished.

A fixed contact 2% preferably of tungsten is integrally secured to the block 15 which is provided with a circular bafile 21 for protecting the fixed end of the switch from impingement of particles traveling at high speed from the contact points when the contacts are opened.

Interposed between the cylindrical sidewall 10 of the switch housing and the fixed endplate 11 is a relatively thin ring 25 of insulating ceramic material which abuts the endplate 11 on one side and which is fixedly secured at its other side to an annular metallic membrane 26, preferably of a nickel iron alloy, which constitutes a sealing ring. Said annular sealing ring is of relatively large internal diameter and is brazed at its internal peripheral margin 2'? to the adjacent inner side of endplate ill. The adjacent annular surfaces of sidewall lit? and ring 25' are metalized to permit the brazing thereto of both sides of the outer peripheral margin of annular membrane 26. At this point it may be noted that the ring 25 is not connected with the endplate ill except that, when the relatively high force exerted by atmospheric pressure is applied, said ring 25 and end plate 11 are eifectively secured together by friction.

A somewhat similar construction is employed at the mobile end of the plate wherein annular membrane 39 is fixedly secured in air tight relation at its inner peripheral margin to the endplate l2 and at its outer peripheral margin to a ceramic ring 31 similar to ring 25. The outer margin of membrane 39 is also secured to the adjacent end of sidewall ill. in this case, however, a corona shield indicated at 32 is brazed at its inner side to the outer periphery of membrane Bil. The corona shield 32 may also be fixedly secured to endplate 12 by brazing as shown in FIG. 1. This assembly that includes the corona shield 32 permits the latter to be added to the assembly after the switch is completed and permits corona shields of various sizes to be substituted, if such substituted becomes necessary, without atfecting the switch assembly.

Extending through the endplate 12 is an operating rod 35 which is slidably secured within a Teflon bearing 36 which in turn is screw threadedly received within a bushing 37 fixedly secured as by brazing to the copper end- Wall 12. By this construction the bearing 36 may be removed and another bearing substituted should this become necessary.

Interposed between the bushing 37 and the opening in endwall 12 into which it is received is the fixed end of a flexible bellows 33 which may be sealed at its inner movable end to an annular plate 39 which in turn is integrally connected to a. relatively heavy contact head 40 which carries to mobile contact 41.

The inner end of the operating rod 35 is provided with an enlarged head which is received within an insulating ceramic block 43. The block 43 is provided with a central countersunk opening in continuation of a smaller opening 45 which receives the operating rod 35 therethrough. By inserting the operating rod 35 through the upper end of block 4-3 and by interposing an insulating spacer 45 between the outer end of the upset portion 42 of rod 35 and the adjacent side of head 4% the operating rod 35 may be effectively held against movement in either direcsassy/15 It is undesirable to permit the bellows 38 to carry any more than a nominal amount of current and for this reason the electrical connection between endwall 12 and the contact head 51 is effected by means of a plurality of flexible conductive straps i8 fixedly secured at one of their ends to end plate 12 by cap screws '4? and at their other ends by means of a peripheral band 52 to the head 4Q. Band 52 may be provided with opposed flanges 54 at its ends to receive a tightening bolt 53 as indicated in FIG. 1.

T he means for shielding the ceramic or glass sidewall ltd from sputter from the contacts 2h, 21 is best seen in FIGS. 1, 2. Such shielding means comprises a plurality of generally cylindrical shielding members 55 which are spaced inwardly from the inner periphery of sidewall it and also axially spaced apart by means which will now be described.

Referring to FIG. 2 a typical pair of adjacent shielding members 55 are shown in their spaced apart relationship. Such spacing is accomplished by means of a plurality of circumferentially spaced apart ceramic elements 56 each of which may comprise a short cylindrical length of ceramic red. Each shielding member is provided with a large diameter portion 5'7 and a small diameter portion 53 with a radially extending annular juncture 59 integrally connecting said portions. t will be seen from FIG. 4 that the spacing between sidewall ll of the housing and the members 55 may be very accurately effected by interposing a plurality of insulating elements 5% between said sidewall and the outer sides of the small diameter portions 53 of the shielding members 55. By predetermining the outer diameter of shielding member 55, and particularly portion 53 thereof, the elements 56 may be interposed between the sidewall and the shielding member with a slight amount of pressure so that the shielding member is retained in fixed relationship relative to sidewall it by its own resiliency.

In order to provide the desired axial spacing between adjacent shielding members $55 a central hole 61 is formed in each spacing element 56) for securely receiving therein a relatively small metallic connector 62 which extends outwardly from element 56 and is fixedly secured as by brazing or welding to the large diameter portion 57 of the adjacent shielding member 55. The adjacent edge of said large diameter portion 57 should abut the element 56 to provide uniform axial spacing.

As can be seen from FlG. l the above described shield ing structure permits a very speedy assembly of the sputter shield in that one member 55 may be inserted from the mobile end of the switch housing so that the large diameter portion 57 bears against the annular sealing membrane 23 thus fixedly positioning the first shielding member relative to the switch housing. The next shielding member 55 may then be inserted into the housing so that the insulating elements 56 are lightly press-fitted between the small diameter portion of the first inserted shielding member and the cylindrical sidewall w, and so that said elements engage the outer side of the annular juncture 59 as best seen in FIG. 2. Since the second inserted shielding member is fixedly secured to the insulating elements 56 carried thereby, the second shielding member 55 is thus accurately spaced apart a predetermined distance from the first shielding member 55.

The above noted procedure is continued until the inner side of the sidewall it) is completely protected along its length by shielding members 55. If required, a portion 65 of a shield may be inserted to take up the space between the last complete shielding member and the above described annular membrane 39 that acts as a seal for the mobile end of the switch.

With reference to Phil. 2, the above described assembly may be facilitated bysightly tapering the small diameter portion 555 of each shielding member 55 so that the diameter of said small diameter portion is slightly greater adjacent the juncture 59 than at the lower free end of the portion. This facilitates insertion of the ceramic elements between the sidewall and the shielding member and at the same time permits a wedging effect to achieve the desired amount of pressure between the assembled parts.

An alternative form of seal for the mobile end of the switch is shown in FIG. 3. In this case the sidewall it? and the ceramic washer Sll may have the same construction as in FIG. 2. However, with the structure of FIG. 3 a combination expansion joint and corona shield Til is provided in the form or an annular membrane, the inner peripheral margin of which is fixedly secured by brazing to the adjacent metalized surfaces of the cylindrical sidewall lti and the ceramic washer 31. The outer peripheral margin of the mebrane '79 is brazed or otherwise hermetically sealed to the endwall 1d of the switch housing. Between said outer and inner peripheral margins of the membrane W) the latter is formed to provide an annular expansion portion 711 of U-shaped section.

It will be noted that both the seal construction of FIG. 1 and that of FIG. 3 provide for relative shifting caused by expansion between the endwalls ll, 12 and the cylindrical sidewalls id in that the ceramic rings 2-5, 31 are permitted to shift radially relative to the adjacent endwalls was to obviate any excessive stresses that might otherwise result from differences in coetficients of expansion of the dissimilar mating materials. It will also be noted that the forces resulting from atmospheric pressure are not imposed upon the sealing membranes in such a manner as to cause excessive strains therein. For this reason the sealing function of the membranes is not impaired. lt will also be noted that the above described structure for connecting the shielding members 55 to the housing is extremely economical to manufacture and to assemble. For example, the shielding members 55 may be drawn from sheet stock and formed on a die and the relatively small identically formed insulating elements 56 may be cut from a length of ceramic rod.

1 claim:

1. In a vacuum switch that includes a vacuumized envelope having a pair of opposite endwalls and a cylindrical sidewall between said endwalls and a pair of coaxial contacts extending into said envelope from said opposite endwalls, shielding means for shielding said sidewall from particles and vapor diffused from said contacts comprismg:

a pair of cylindrical shielding members having overlapping portions concentric with and inwardly of said sidewall, and

' a plurality of insulating elements interposed between said sidewall and said overlapping portions of said shielding members at circumferentially spaced points around the periphery of the latter for supporting said members relative to said sidewall,

said insulating elements being press-fitted betweensaid sidewall and said members whereby the latter are held in a predetermined position relative to said sidewall by the inherent resiliency of said members.

2. in a vacuum switch that includes a vacuumized envelope having a pair of opposite endwalls and a cylindrical sidewall between said endwalls, and a pair of coaxial contacts extending into said envelope from said opposite endwalls, shielding means for shielding said side wall from particles and vapor diffused from said contacts comprising:

a pair of axially spaced apart cylindrical shielding members concentric with and inwardly of said sidewall,

a plurality of insulating elements interposed between said sidewall and one of said members at spaced points around the periphery of the latter for supporting said one member relative to said sidewall, and

a metallic connector connected at one of its ends to one of said elements and secured at its other end to the other of said pair of members for securing said pair of members in axially spaced relationship.

3. A device as recited in claim 2 in which the diameter of said one member at said elements is less than the diameter of the adjacent portion of the other of said members and said adjacent portion is interposed between said side wall and said one member.

4. In a vacuum switch that includes a vacuumized envelope having a pair of opposite endwalls and a cylindrical sidewall between said endwalls and a pair of coaxial contacts extending into said envelope from said opposite endwalls, shielding means for shielding said sidewall from particles and vapor diffused from said contacts comprising:

a plurality of similar axially spaced apart cylindrical shielding members concentric with and inwardly of said sidewall,

each of said members including a small diameter portion and a large diameter portion with the small diameter portion of one member of a pair of adjacent members received within but spaced from the large diameter portion of the adjacent member of such pair,

a plurality of ceramic insulating elements interposed between said sidewall and the small diameter portion of one member of each pair of members at spaced points around the periphery of said one member for supporting said one member relative to said sidewall,

each of said elements being provided with a metallic connector connected at one end to the element and secured at its opposite end to the large diameter portion of the adjacent member for securing said adjacent pair of members together.

5. An envelope for a vacuum switch and the like comprising:

a pair of opposite end walls of conductive material,

a cylindrical sidewall of insulating material positioned between said endwalls and cooperating with said endwalls to form a generally cylindrical envelope,

a ring of insulating material outside said envelpes in sliding engagement at its outer side with one of said endwalls,

an annular sealing membrane of conductive material hermetically sealed at its inner peripheral marginal portion to said endwall within the envelope and with its outer peripheral marginal portion interposed between said ring and the adjacent end of said sidewall the outer periphery of said annular sealing membrane lying within the outer periphery of said cylindrical sidewall and said ring of insulating material, and

means hermetically sealing said outer peripheral marginal portion to said adjacent end of said sidewall and to the inner side of said ring whereby said ring is isolated from the vacuum within the envelope.

6. An envelope according to claim 5 wherein an annular corona shield surrounds said one end wall and said ring and is fixedly secured to the outer marginal edge of said annular sealing membrane and to said one endwall.

References Cited by the Examiner UNITED STATES PATENTS BERNARD A. GILHEANY, Primar y Examiner. ROBERT K. SCHAEFER, Examiner. 

1. IN A VACUUM SWITCH THAT INCLUDES A VACUUMIZED ENVELOPE HAVING A PAIR OF OPPOSITE ENDWALLS AND A CYLINDRICAL SIDEWALL BETWEEN SAID ENDWALLS AND A PAIR OF COAXIAL CONTACTS EXTENDING INTO SAID ENVELOPE FROM SAID OPPOSITE ENDWALLS, SHIELDING MEANS FOR SHIELDING SAID SIDEWALLS FROM PARTICLES AND VAPOR DIFFUSED FROM SAID CONTACTS COMPRISING: A PAIR OF CYLINDRICAL SHIELDING MEMBERS HAVING OVERLAPPING PORTIONS CONCENTRIC WITH AND INWARDLY OF SAID SIDEWALL, AND A PLURALITY OF INSULATING ELEMENTS INTERPOSED BETWEEN SAID SIDEWALL AND SAID OVERLAPPING PORTIONS OF SAID SHIELDING MEMBERS AT CIRCUMFERENTIALLY SPACED POINTS AROUND THE PERIPHERY OF THE LATTER FOR SUPPORTING SAID MEMBERS RELATIVE TO SAID SIDEWALL, SAID INSULATING ELEMENTS BEING PRESS-FITTED BETWEEN SAID SIDEWALL AND SAID MEMBERS WHEREBY THE LATTER ARE 